1. Field of the Invention
The invention relates to an environmentally degradable polymer composite, and more particularly to an environmentally degradable composite produced by a renewable raw material and a moderately cross-linked aliphatic polyesteramide as well as a method for producing the same.
2. Description of the Related Art
Currently, the application of large amounts of high performance and cheap petrochemical plastics has seriously polluted the environment. Furthermore, global oil resources are depleted with passing day. Thus, to produce environmentally degradable products with renewable resources are an ideal choice to solve environmental and energy crisis.
Natural polymer materials, such as starch, cellulose (such as bamboo powder, straw power, bagasse), and lignin (such as wood flour), are rich in nature. They are cheap, renewable, and can be used for producing biodegradable materials. However, if the material is processed alone, the resultant degradable plastics have bad service performance. Newly-synthesized degradable plastics, such as aliphatic polyester, aliphatic-aromatic copolyester, and aliphatic polyesteramide, generally have good mechanical properties and service performance, but they are expensive. Thus, to produce an environmentally degradable composite with a cheap renewable raw material and high performance of polymers is a good means to solve the problem of properties and cost, and it has become an important research area of environmentally degradable materials.
Some literatures have disclosed the production of environmentally degradable composites with renewable raw materials and polymers. Mater-Bi, manufactured by Italian Novamont Co., Ltd., is made from starch and polycaprolactone (Catia B. Polymer Degradation and Stability, 1998, 59 (1-3): 263-272). The melting point of polycaprolactone is merely 60° C., which means the product can only be used at an environment with a temperature of 0-50° C. and a relative humidity of 30-80%. In low temperature, high temperature, and high humidity environments, the product is not practicable. Furthermore, Mater-Bi is very expensive, with a price exceeding 7,000 USD/ton. Among aliphatic polyester, polylactic acid has high melting point and excellent properties. Sun X Z (Kansas State University) et al mix natural starch with polylactic acid, but the compatibility thereof is bad, and the resultant product has unstable properties (Sun X Z. Applied Polymer Science, 2002, 84: 1257-1262).
Aliphatic polyesteramide is a copolymer of aliphatic-aromatic copolyester and aliphatic polyamide. It exhibits superior strength and mechanical properties in contrast to pure polyesters. Due to the coexistence of ester bond and amide bond, polyesteramide has amphiphilic properties. Thus, polyesteramide is more compatible with natural polymers than polyester. As long as the degree of polymerization of the polyamide block of the copolymer is less than 20, polyesteramide can be completely degraded in the environment. Although Chinese Patent Publication No. CN1242032A and CN1222171A disclose the composite of starch and polyesteramide, the properties thereof are not described in detail.